Multiplex telegraphy.



F. K. VREELAND.

MULTIPLEX TELEGRAPHY.

APPLlCATION FILED JAN. 8, 1910.

1,171,81 3. Patented Feb. 15, 1916.

UNITED STATES PATENT @FFICE.

FREDERICK K. VREELAND, 0F MONTCLAIR, NEW JERSEY, ASSIGNOR TO VREELAND APPARATUS COMPANY, INC., 01? NEW YORK, N. Y., A CORPORATION OF NEW YORK.

MULTIPLEX TELEGRAPHY.

Specification of Letters Patent.

Patented Feb. 15, 1916.

Application filed January 8, 1910. Serial No. 536,963.

broadly the basic features of my system of, multiplex telegraphy, in which a number of f alternating currents of d1lIE18l1t frequencies are simultaneously impressed upon a common line and selectively received by a number of receiving units, each tuned to respond to one of the transmitted frequencies.

In the present application, I desire to set forth more fully and claim specifically some of the features contained in the former application, and to describe certain additional features-which tend to simplify the apparatus and to increase its effectiveness.

' In the drawing Figure 1 represents diagrammatically a single sending and receiv ing unit inwhich certain of these improvements are embodied through the agency of a double contact key. Fig. 2 represents a similar arrangement in which a transmitter relay operated by a local battery is substituted for the double contact key. Fig. 3 shows the manner in which the different parts of the apparatus are distributed in an installation involving a large number of units. Fig. at represents a modification in the sending and receiving unit whereby the constructionof the sifting circuit is simplified and its effectiveness increased.

In Figs. 1, 2 and 4, a single unit is shown, it being typical of a number of similar units which in practice will be similarly connected to the line. In Fig. 3, two units are shown,

for simplicity, in place of the large number which would usually be employed.

In the figures, I have used as far as possible the same letters and numbers to designate the different parts of the apparatus as I used in the former application to designate parts'which perform similar functions.

Referring to the drawing, Fig. 1 represents an .improved arrangement for coupling the oscillator or equivalent alternating current generator to the line, and breaking up the currents impressed on the line into signal impulses. It also shows an improved method of regulating the relative intensities of the sent and received signals as they are heard by the operator. In this arrangement, the coupling circuit which in some cases is used tocouple the oscillator to the sifting cir-' cult, is omitted, and the sending key, K, is I located directly in the sifting circuit In order that the continuity of the sifting circuit may not be materially interrupted, the key is provided with two contacts, one of which, a, is used for impressing the signal impulses on the line, and the other, 7), for permitting the passage of received impulses coming from the distant end of the line.

The branch circuit controlled by. the contact a, includes a secondary coil, 8,, through which energy is received from the oscillator and another coil P which is inductively coupled to the resonant receiving circuit, 8 R. The coil S is shown in the. diagram as being inductively coupled to the primary coil,P which is included in the oscillating circuit, P,(;,L,, of the oscillator, O,this being one of several arrangements by which energy from the oscillator is impressed on the sifting circuit.

The second contact, I), of the key, K, is connected to a second primary coil, P which is also inductively coupled to the resonant receiving circuit, 8 R. Both of the alternative branch circuits, K a 8,1 and K 2) P are connected to the sifting circuit, (1 L, This sifting circuit is designed according to the principles set forth in the former application.

The operation of this apparatus is as follows: In the normal position of the key, when signals are not being sent, it makes contact with the point b, so that signal impulses of the proper frequency coming over the line will traverse the sifting circuit which istuned to this frequency, through the primary coil P,,,. This primary coil acting inductively through the loose coupling, P,,, S,,, excites resonant oscillations in the receiving circuit, S 1 which is also tuned and is sharply selective to the proper frequency, and the induced currents are detected by the electrostatic telephone, or equivalent receiving device, R, which, in the arrangement here shown, combines the functions of condenser and receiver. ll hen the key, K, is depressed, it opens contact with the point 6 and makes contact with the point a, thus completing the sifting circuit through the branch (1 S P Which is coupled to the oscillator O, and impressing a signal current 'upon the line. This signal current in trava smaller number of turns than the coil P or by coupling it more loosely to the coil In practice, it is desirable to have an adjustable coupling between both of the primary coils and'the secondary, although the recei er primar P may be fixed in relation to he secon ary, S and the transmitter primary, P i, ,adjustable. The apparatus may then be, adjusted so that the sent signals have the same apparent intensity as the received signals, or a greater or less intensity, as desired. The adjustment of the transmitter primary is desirable, in order that the proper relation of transmitted to received signals may be secured whether the line is long or short, in etlicient working condition or otherwise. \Vhen the coupling between the receiver primary, 'P and the secondary, S is non-adjustable,- it should be madeas close as is compatible with the desired selectivity, in order that the intensity of the received signals may not be unduly sacrificed. 'Inany case, however, the coupling is a loose one.

' Fig. ;2 represents a similar arrangement in which a' transmitter relay. T .having double contacts, and I), is substituted for the double contact'key,:K. The relay T is operated by local battery, Ba, controlled by a single contact key, K. The sending contact, a, of the relay 'is made flexible by means of a spring, (1, attached tothe armature or'by equivalent means, so that the durationgof the Contact with the point a is longer than the \contact of the key K. This slight sluggishness has the eiiectof lengthening the Fdot or short signal impulse, which is often desirable fo 1"-"i'api(l signaling, inasmuch; as

p it allowsalonger-time forthe signal current to buildup inthc resonant circuit, thusmaking'the intensity of the dot equalfor {nearly so, t'o'the intensity of the dashQIt'isfnot 'always' desirable,however, to ma'ke the apparent intensity of the .dot quiteequ'al' to that of the dash, since a slight difference of intensity 'makes the signals more easily differentiat'ed and read. The duration of the contact at a may be controlled by adjusting the tension of the spring 0!, the weight of the movingelement of the, relay, the pull of the magnet or the position of the contacts.

In an installation which comprises a large number of sending and receiving units, it is desirable to separate the different parts of the apparatus for the sake of simplicity at the operating table and convenience of control and adjustment. Fig.3 shows a suitable subdivision, in which all the oscillators are concentrated in a generating plant, G, (which is here represented for simplicity by two units only), and all the sifting circuits are concentrated in a sifting equipment,,E. Three wires, 1, 2' and 3', run from this centralized equipment to each of the operating sets, of which two are represented, A

and B. The generating plant andsifting circuits are located at a central station, while the operating sets, A and B, may be distributed at any convenient points at a distance from the central station, or they may be grou ed together in a single operating room. oscillators are preferably permanently adjusted, and the sifting circuits are permanently tuned, respectively, to these frequencies, although means should be provided for the initial adjustment of the tune. The,only adjustment remaining at the operating table is that of the resonant receiving circuit, and the adjustment of the coupling which controls the relative intensities of the sent and received signals. The operating apparatus isthus greatly simplified and the removal of the sifting circuits from the operating tables prevents an operator from tuning to any frequency other than his own.

Fig. 4 represents an improved method of coupling the sifting circuit to the line. As I have stated in the former application, the sifting circuit should have an unbalanced reactance for the nearest foreign frequency which is large compared to the equivalent impedanceof the line, it being understood that this term equivalent impedance includes not only the quantity'ordinarily known as the line impedance,which 'depends only'upon the line constants per unit length and not upon the length of theline, but includes also the line attenuation. Equivalent impedance as the term is used he frequencies of the different- I here and in'the former application, there- -fore, depends upon the length oftheline.

It is thus necessary on long-lines to have a large unbalanced'reactance in the sifting circuit. Where the frequency difference is small, this means that when thesifting 'circ'uitis "directly? connected to .the "line its self induction must be-fvery large and its capacity very small, hence for"lon'g lines, Where the attenuation is considerable and "a considerable current must be impressed on the line, the inductive drop across the ini be required of the sifting circuit reactance ductance and the voltage across the condenser of the sifting circuit may become very high, thus necessitating the subdivision of the circuit into several capacity and inductance units, in order to secure the requisite insulation. These high voltages may be avoided without diminishing the unbalanced reactance of the sifting circuit system with reference to the line by connecting the sifting circuit to the line, not by a direct metallic connection, but through a transformer p 8, whose winding 79 has a larger number of turns than the winding .5. The winding 22 is shunted across the line and the winding .9 is connected in the sifting circuit. The winding 7) acts as primary when receiving and as secondary when transmitting signals, and the winding 8, vice 'versa. -The ratio of transformation is such that the current in thecoil s is larger than that in the coil 79, and the voltage is correspondingly small. Thus the inductance, L of the sifting circuit may be made relatively small and the capacity, C correspondingly large. The unbalanced reactance of the siftingv circuit with reference to the line will however still be large, since the actual reactances must be multipliedby the square of the ratio .of transformation, that is, usually, by the square of the ratio of the turns of the coil 7) to those of the coil 8.. The reactance of the coil 7) alone, on open circuit, should be large with reference to the equivalent line impedance, since the reactance of the system as a whole'can never be greater than the' reactance of the coil 7) on open secondary circuit. The reactance of the coil '7) may however be very much smaller than would if the sifting circuit were directly connected to the line. The transformer, 12 s, is preferably a close coupled one, since it is desirable to'have the reactance of the coil 79 completely annulled by the influence of the secondary oscillations when the secondary or sifting circuit is tuned to the proper fre quency. The primary coil thus permits the passage of received signal impulses of the proper frequency without opposition, while excluding, by virtue of its uncompensated reactance, currents of any other frequency.

This feature of the step-down transformer may be applied to any of the arrangements described in this or the former application in place of the direct shunting of the sifting circuit across the line, the coupling through a transformer with shunted primary being equivalent to a shunt connection, due allowance being made for the ratio of transformation.

In the claims, for convenience, the winding connected to the line is arbitrarily called the primary and the other winding the secondary, and a transformer whose )rimary or line winding is the larger is called a stepdown transformer, it being understood that these conditions are reversed when sending.

\Vhat I claim is: I

1. In a system of multiplex telegraphy by alternating currents of different frequencies, the combination with a line, of transmitters and selective receivers associated therewith, and means whereby each receiver is made sensitive to distant impulses of definite frequency and less sensitive to impulses of the same frequency from its companion transmitter, substantially as set forth.

2. In a system of multiplex telegrap'hy by alternating currents of different frequencies, the combination with a line, of tuned sifting circuits in parallel relation thereto, alternating current generators and selective receivers associated with said sifting circuits, and circuit controllers located in the sifting circuits for translating the generator currents into signal impulses, such circuit controllers making the receivers sensitive to distant signalswhen signal currents from their come paniongenerators are interrupted. and less sensitive to signal currents from their companion generators, substantially as set forth.

3. In a system of multiplex telegraphy by alternating currents of different frequens cies. the combination with a line. of tuned sifting circuits in parallel relation thereto and transmitters and receivers associated with said sifting circuits and with each other. each receiver being coupled to the line for receiving distance signals and more feebly coupled to its companion transmitter for receiving transmitted" signals. substantially as set forth.

4. In. -.a. system. of multiplex telegraphy by alternating currents of different frequencies. the combination with a line. of tuned sifting circuits in parallel relation thereto, transmitters associated with said sifting circuits. receivers associated with said sifting circuits and connected to the line separately from their companion transmitters,

such receivers being also connected inductively with their companion transmitters, and circuit controllers opening and closing alternately the circuits of companion trans- .mitters and receivers, substantially as set cies, the combination with a line, of a transformer of unequal windings having itsliigh voltage winding connected with the line,

and {a timed sifting circuit 'connected 'with the 'lowvoltage winding of the transformer and 'liaving when thus connected alarge unbalanced reactance for small frequency differences relative to the equivalent line impedance, substantially as set forth.

9; In a system of multiplex telegraphy by alternating currents of different 1 frequen cies, the combination with a line. of a'transformer-of unequal windings having its high 25- voltage winding connected with the line, a timed sifting circuit connected'with the low voltage winding of the transformer and having when thus connected a large unbalanced reactance for small frequency differences relative to the equivalent line impedance, and signal transmitting apparatus, including a generator of'alternating currents, associated with saidsift ng circuit, substantially as set forth.

10. In asystem of multiplex telegra-pliy by alternating currents of different frequencies, the combination with a line, of a:

transformer ofunequal windings having its highvoltage winding connected with the line, a tuned sifting circuit connected with the low voltage winding of the transformer and .having when thus connected a large unbalanced reactance for small frequency differences relative to the equivalent line impedance, and signal transmitting and receiving apparatus, i eluding a generator of alternating current and a selective receiver, associated with said sifting circuit,

substantially asset forth. a

l1. In a system of multiplexte'legraphy by alternating currents, the combination with aline, of a transformer of unequal windings having an un'tuned 'high voltage? winding connected with the line, and a tuned resonant circuit connected with the low voltage winding of the transformer, substantially as set forth.

12. In a system of multiplex telegraphy by alternating currents, 'the combination with a li ne of a transformer of unequal receiver connected with the said tuned circuit, substantially as set forth.:-;"=

'13. In a system of multiplex-tele'graphy by alternating currents, the combinationw with a line, of a transformerwof, unequal;

windings having an untuned high voltagewinding connected with the line, "a tuned resonant circuit connected with the lowv voltage winding of the transformer-and a generator of alternating currents connected with the said tuned circuit, substantially as set forth. a

14. In a system of multiplex telegraphy by alternating currents, the combination with a line, of a transformer of unequal windings having an untuned high voltage winding connected with the line, a tuned resonant circuit connected with the low voltage winding of the transformer, a receiver connected with the said tuned circuit and a generator of alternating currents also connected with'said tuned circuit, substantially as set forth. a i This specification signed and witnessed this fourth day of January, 1910..

FREDERICK K. VREELA'ND.

Witnesses:

JOHN L. Larson, P. T. WARD. 

